undercover investigation has prompted action by federal investigators. They have shut down a supplier for a popular burger chain in-n-out burger whose tag line is quality in everything. Here's brian ross. Reporter: With the quality you can taste, the west coast in in-n-out burger. Hollywooders caught miley cyrus and her family pulling in for their burgers. Today, the fabled chain was fighting a public relations nightmare after an animal rights group shot this video in june and july of this year at a meat company that supplies at much as 30% of their meat. What our investigators posed who could not walk out they are being prodded, jabbed. Reporter: Under federal law, cows not able to walk on their own are considered potential food safety rink and should not be used for food consumption. Animals who are not ambulatory do not have a disease, there are word that mad cow disease may escape detection. Reporter: After viewing the video, federal inspectors came to the plant yesterday and ordered it shut down based on what they said was inhuman treatment of the animals. The inspectors said they did not find any diseased animals nor did they order a recall of the meat from the plant. Investigators said they were cooperating but surprised by the allegations because usda inspectors operate continuously at the plant and had not found anything wrong previously. It is true, in fact, that usda inspectors were onsite for this and that is something that the usda needs to answer for. As for in-n-out burger, they told us they pay premium for their meat. That company has many other customers, including the usda's national school lunch program. And as of tonight, diane, no word what will happen with that contract eye were the usda. We'll be checking in. Thanks so much, brian.

This transcript has been automatically generated and may not be 100% accurate.

Closer Look at Mad Cow Farm

USDA inspectors visit California dairy farm where case was reported.

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